Lithiomarsturite, LiCa2Mn2Si5O14(OH)

• Main Authors: Hexiong Yang, Robert T. Downs, Yongbo W. Yang
• Format: Article
• Language: English
• Published: International Union of Crystallography 2011-12-01
• Series: Acta Crystallographica Section E
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S1600536811047581

Lithiomarsturite, ideally LiCa2Mn2Si5O14(OH), is a member of the pectolite–pyroxene series of pyroxenoids (hydropyroxenoids) and belongs to the rhodonite group. A previous structure determination of this mineral based on triclinic symmetry in space group Poverline{1} by Peacor et al. [Am. Mineral. (1990), 75, 409–414] converged with R = 0.18 without reporting any information on atomic coordinates and displacement parameters. The current study redetermines its structure from a natural specimen from the type locality (Foote mine, North Carolina) based on single-crystal X-ray diffraction data. The crystal structure of lithiomarsturite is characterized by ribbons of edge-sharing CaO6 and two types of MnO6 octahedra as well as chains of corner-sharing SiO4 tetrahedra, both extending along [110]. The octahedral ribbons are interconnected by the rather irregular CaO8 and LiO6 polyhedra through sharing corners and edges, forming layers parallel to (overline{1}1overline{1}), which are linked together by the silicate chains. Whereas the coordination environments of the Mn and Li cations can be compared to those of the corresponding cations in nambulite, the bonding situations of the Ca cations are more similar to those in babingtonite. In contrast to the hydrogen-bonding scheme in babingtonite, which has one O atom as the hydrogen-bond donor and a second O atom as the hydrogen-bond acceptor, our study shows that the situation is reversed in lithiomarsturite for the same two O atoms, as a consequence of the differences in the bonding environments around O atoms in the two minerals.